Cloudy apple juice has been treated by high pressure carbon dioxide (HPCD) as non-thermal technology to inactive polyphenoloxidase and pectinmethylesterase in batch mode. Stirring speed (from 200 to 600 rpm) induced an increase in the enzyme inactivation rate while a triple cycle of pressurization/depressurization led to the same enzyme inactivation efficiency. Enzyme inactivation kinetics were determined at different temperatures (from 35 to 45 ºC) and pressures (from 10 to 20 MPa). Data were described by the first order kinetic model and the Weibull model. For the first order kinetic model, decimal reduction time for HPCD treatment was found to be smaller than for mild heating, in the same temperature range. The same tendency was observed for the first decimal reduction time in the Weibull model. HPCD treatment resulted in a homogenization effect reflected in the shifting of the particle size distribution towards smaller diameters after treatment. HPCD treatment did not result in a change of water and oxalate soluble pectin content, total phenolic compounds and hidroxymethylfurfural content.
Cloudy apple juice has been treated by thermosonication in batch mode as an alternative processing to thermal treatment. Thermosonication was found to be effective to inactivate polyphenol oxidase; however, pectinmethylesterase was found to be more resistant. An increase of the working ultrasound amplitude and the amount of energy supplied to the juice led to lower enzyme residual activities.Enzyme inactivation kinetics were determined at different temperatures (from 44 to 67 ºC).Inactivation data were described by the first order kinetic model and the Weibull model, both models yielding good fitting. Thermosonication treatment caused a homogenization effect reflected in the shifting of the particle size distribution towards smaller diameters. The effect of the nature of dissolved gases in the juice on enzyme inactivation was studied by displacing the air dissolved in the juice by bubbling nitrogen or carbon dioxide, previous to the thermosonication experiments. Higher inactivation rates were obtained by displacing the air with nitrogen.Industrial relevance: Consumers demand of natural and fresh-like products has driven the food industry to investigate alternative technologies to replace conventional food heat treatments that may affect food quality. Among these technologies, thermosonication treatment is an attractive technology that can inactivate microorganisms and enzymes. This work shows that some enzymes that cause deleterious effect on cloudy apple juice can be more effectively inactivated by thermosonication than by thermal treatment, in the same temperature range, reducing the damages caused by heating
6Inactivation of pectinmethylesterase (PME) and quality parameters of orange juice have been 7 studied after high pressure carbon dioxide (HPCD) treatment. The HPCD treatment conditions 8 covered a wide range of temperature from 2 to 40 ºC, far below normal thermal treatment, while 9 operating pressure was varied from 10 to 30 MPa and exposure time from 3 to 60 min. A 10 decrease in PME activity was found, even at the lowest temperature studied in this work, 2 ºC. 11Different inactivation kinetic models were used to correlate the PME residual activity: the two-12 fraction model, the fractional-conversion model and the Weibull model. The two-fraction model 13 presents the lowest mean relative deviation. Some quality parameters such as colour, pH, ºBrix, 14 turbidity, ascorbic acid, total acidity and particle size distribution (PSD) were also determined 15 right after HPCD treatment and along storage at 4ºC up to 12 days. PSD shows that HPCD 16 treatment results in a volume increase of small particles and a volume decrease of large particles
Tomato juice, Lycopersicon esculentem cv. Canario, has been treated by HPCD as non-thermal preservation treatment. The inactivation kinetics for pectinmethylesterase (PME) and polygalacturonase (PG) were determined at different pressures (8.5 to 20 MPa) and temperatures (35 to 55 ºC). At the highest operating pressure and temperature essayed in this work, it was found that PME could be almost completely inactivated, whereas PG resulted to be more HPCD resistant at the working conditions. PME enzyme inactivation curves were properly described by a Weibull type model, while the fractional conversion model was the most appropriate for the PG with a sharp initial decrease in activity. On the contrary, high hydrostatic pressure led to a nearly complete inactivation of PG while PME was very resistant at 600 MPa. It was also found that HPCD treatment led to a smaller particle size distribution of tomato juice.
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